1. Field of the Invention
This invention relates to a Geneva drive mechanism including a driven member defining arcuate recesses and radially outwardly opening slots arranged in a rotating direction, and a driving member having an engaging element for engaging the slots of the driven member to rotate the driven member intermittently by a predetermined angle.
2. Description of the Related Art
The Geneva drive mechanism has a function to convert continuous rotation into intermittent rotation by a set angle. That is, when a continuous rotation is inputted, the Geneva drive mechanism outputs an alternate repetition of rotation and stoppage, i.e. a rotation through a set angle followed by a stopping period, and then a rotation through the same set angle.
Generally, this type of Geneva drive mechanism includes a driven member defining arcuate recesses and radially outwardly opening slots arranged alternately at predetermined intervals circumferentially of the driven member, and a driving member for intermittently rotating the driven member. Such a Geneva drive mechanism is disclosed in Japanese Utility Model Publications Kokai No. S60-64357 and No. H6-40507, for example. In the prior constructions disclosed therein, the driving member includes an engaging roller acting as the engaging element for successively engaging a plurality of slots in the driven member to rotate the driven member intermittently by a predetermined angle. This driving member further includes a plurality of turn rollers rotatable about pivotal axes fixed to the driving member for contacting arcuate surfaces of the arcuate recesses in the driven member when the engaging roller is disengaged from the slots so that the driven member does not rotate with the driving member.
In the Geneva drive mechanism having the above construction, when, with rotation of the driving member, the engaging roller engages one of the slots in the driven member, the driven member is rotated until the engaging roller is disengaged from the slot. Thereafter, the rotation of the driven member is suspended until the engaging roller engages the next slot in the rotating direction.
With the driven member at rest, the turn roller of the driving member, while contacting the arcuate surface of one of the arcuate recesses of the driven member, rotate about the pivotal axes and move with the driving member along the arcuate surface.
According to the conventional Geneva drive mechanism, as noted above, when the driven member is at rest and the driving member is in rotation, the turn rollers move along the arcuate surface one of the arcuate recesses of the driven member. The driving member may include a cam defining a rotation restricting surface movable in sliding contact with the arcuate surfaces of the arcuate recesses of the driven member at rest (see FIG. 4 of Japanese Utility Model Publications Kokai No. H6-40507, for example). Compared with this construction, the foregoing construction has an advantage of reducing friction between the driving member and the driven member when the latter is at rest during intermittent rotation. With the reduced friction, the driving member is smoothly rotatable free of seizure, the Geneva drive mechanism has an extended life, and a reduction in energy consumption may be achieved in relation to rotation of the driving member itself.
However, in the conventional Geneva drive mechanism, a reaction is applied between the turn rollers and the pivotal axes of the driving member rotatably supporting the rollers when the rollers in rotation move with the driving member along the arcuate surfaces of the driven member. The positions where the reaction is applied are subjected to a strong frictional force. Thus, there is room for improvement in achieving an extended life of the Geneva drive mechanism as well as energy saving.